Scores of health magazines and fitness apps advise users how to maintain a healthy body mass index. But forget about BMI for a second, and consider another acronym: BPI, or brain performance index.

While targeting BMI with trips to the gym may seem like part of another forgone New Year’s Resolution, the Lumosity app lets you exercise your mind on the go, improving your BPI – a term coined by Lumosity – with a few fun games a day, conveniently through your iPhone. And, as of Thursday, Lumosity now has an iPad counterpart, so that the brain calisthenics can continue in tablet format. On a downside, there is currently no Lumosity app for Android products.

The BPI scales are based on more than 13,000,000 real game results, according to the company. The program uses game results to create a distribution of scores for each activity, and then measure how an individual score stacks up. An algorithm then derives your BPI.

The program is like a “gym for your brain,” says Lumosity chief executive Kunal Sarkar in a statement. The free application boasts 20 million downloads, and currently occupies the coveted position as the No. 1 Education App on the USiTunes App Store and in nearly 40 countries worldwide. For an extended version of the service – meaning more gaming opportunities – users can open a subscription at the cost of $14.95 per month for the online service, or $80 a year for the iPhone and iPad app.

Though the games might be challenging, Lumosity is surprisingly easy to use, thanks to an updated interface that rolled out in June.

Users download Lumosity in the App Store, register with an e-mail address, and then answer a series of questions to personalize the learning experience.

There are five categories of brain training: Memory, Attention, Speed, Flexibility, and Problem Solving. Users can select if they want to better recall the location of objects, learn to remember names after first introductions, multi-task more effectively, or make more logical decisions. In under a minute – and with a few clicks – the app devises a personalized training schedule. And in our play tests, the regime is, well, fun, with games like Pinball Recall to train memory and Spatial Speed Match to help users think more quickly.

Though Lumosity aims to reach users of all ages from a wide variety of educational backgrounds, the application's popularity is part of a larger trend of incorporating educational components into video games for classrooms. A 2008 Pew Research study showed that 97 percent of teens ages 12-17 play video games, or portable games. And groups such as the Institute of Play have been teaming up with teachers to harness students' love of the digital into enthusiasm for education. Games like Lumosity offer a way to keep students – and their parents – engaged in learning games beyond the school day.

The Lumosity application was designed by a team of neuroscientists and cognitive psychologists from Stanford University and the University of California – San Francisco, and was launched in 2007. At the time of its launch, more than 95 percent of users “considered the program to be fun.” Today’s 40 million registered Lumosity users might be inclined to agree.